<check-sources> Clean up long lines, unpythonic names

First big pass with pylint to bring code close to PEP 8 style. Should
be no logical changes other than `OpenShiftCheckSources._init_yumbase`
returning the yumbase object instead of setting `self.yum_base`
directly.
Merge pull request #168 from dobbymoodge/check-sources-cleanup

<check-sources> Clean up long lines, unpythonic names, etc.
<oo-admin-check-sources> Bug 1028572 - uniquify flatten results
https://bugzilla.redhat.com/show_bug.cgi?id=1028572

This bug was caused by `flatten()` allowing duplicate values in its
results. Wrapped returned list in `list(set())` to guarantee
uniqueness
Merge pull request #170 from dobbymoodge/BZ1028572

<oo-admin-check-sources> Bug 1028572 - uniquify flatten results
<check-sources> Bug 1028612, fix excludes list building logic, RHN code
https://bugzilla.redhat.com/show_bug.cgi?id=1028612

List `need_exclude` in `set_excludes` wasn't being built properly, it
failed to filter by repos which already had excludes set. Added
`_excludes_needed` helper function to build this list.

`set_save_repo_attr` in `OpenShiftCheckSources` didn't handle writing
configs from iterables for RHN correctly. Added simple logic to munge
`value` variable if it's iterable

Also included several spelling, formatting and minor refactors from
code review with Miciah.
Merge pull request #173 from dobbymoodge/BZ1028612

<check-sources> Bug 1028612, fix excludes list building logic, RHN code